August 31, 2021
The outer protection structure of modern buildings generally no longer uses traditional brick walls and block bricks, but uses architectural curtain walls. Building curtain walls include glass curtain walls, stone curtain walls, aluminum curtain walls, ceramic board curtain walls, clay board curtain walls, metal board curtain walls, fiber cement board curtain walls and other board curtain walls. Building curtain walls have many advantages such as beautiful appearance, energy saving, and easy maintenance. The joints between the panels need to be sealed with silicone weathering sealants. Silicone weathering sealant needs to withstand the displacement of the joint width caused by the external environment (thermal expansion and contraction of the plate material, displacement of the main structure, etc.) caused by the external environment of the building joint during the application process. This requires the silicone weather-resistant sealant to have a good ability to withstand joint displacement, and to withstand long-term joint width changes without cracking. The displacement ability of silicone weathering sealant is generally 20, 25, 35, 50, 100/-50, etc. For example, level 35 is able to withstand changes in the width of the sealant gap between ±35%. When the silicone weathering sealant is directly exposed outdoors, it must be able to ensure the air-tightness and water-tightness of the curtain wall for a long time. It has very high requirements for its key technical indicators such as elasticity (displacement capacity) and aging resistance.
In the context of the current price increase of raw materials, a considerable number of oil-extended silicone weather-resistant sealant products have appeared on the market, attracting users at low prices. After 5000 hours of UV aging and 70°C, 14 days of heat aging, the oil-extended sealant exhibits a decrease in elasticity and an increase in hardness. The performance decline is very obvious. It cannot meet the corresponding standard requirements of sealants and will directly cause serious quality problems and even safety to users. Hidden danger!
In today's article, we will give you a detailed introduction to the hazards of oil-extended silicone weathering sealants, and share the "film method" of identifying oil-extended adhesives and the performance of oil-extended silicone weathering sealants on the film.
1. The harm of oil-filled silicone weatherproofing sealant
The oil-filling of silicone weather-resistant sealant will cause cracking, chalking, hardening, and oil flow problems of the weather-resistant sealant, leading to premature failure of the sealant, resulting in water leakage and air leakage in the curtain wall, increased energy consumption, and affecting normal use. The oil-filled silicone weather-resistant sealant appears cracking, hardening, or even chalking, which will harm the curtain wall, as shown in the figure below.
figure 1 Cracking and hardening of oil-filled weather-resistant adhesive on aluminum curtain wall of a building
figure 2 Cracking and hardening of oil-filled weather-resistant adhesive on aluminum curtain wall of a building
Oil-filled silicone weather-resistant sealant can also cause penetration pollution to stone and aluminum plates. This kind of pollution is different from vertical flow pollution, it is irreversible and cannot be removed by cleaning.
figure 3 Stone curtain wall pollution caused by oil-filled silicone weathering sealant in a building
figure 4 A building's aluminum curtain wall pollution caused by oil-filled silicone weather-resistant sealant
When the oil-filled silicone weather-resistant sealant is in contact with the insulating glass for a long time, the filled industrial white oil will gradually migrate and penetrate into the insulating glass, causing a sealing butyl sealant of the insulating glass to be dissolved and the phenomenon of oil flow and rainbow will appear, destroying the original insulating glass. Some functions such as energy saving, heat preservation, light transmission and heat insulation.
figure 5 Cracking of oil-filled silicone weather-resistant sealant and oil flow and rainbow phenomenon in insulating glass
figure 6 Film test comparison between oil-filled (left) and non-oil-filled sealant (right)
Looking at the results the next day, the surface of the film on the left is not flat, and the probability of adding mineral oil to the sealant in contact with it is very high. On the contrary, the film on the right side remains flat, and the sealant in contact with it is not filled with oil. The more oil-filled, the more obvious the film shrinks.
Collected 6 different brands of silicone weather-resistant sealant samples from the market, and tested them with the film method. It was found that 3 brands of sealant samples could cause film shrinkage, and the detection rate was as high as 50%, as shown in the figure below:
Figure 7 A certain brand of white silicone weather-resistant sealant
figure 8 A certain brand of black silicone weather-resistant sealant
When testing with the film method, it is found that when the plastic film shrinks and wrinkles, the probability of filling with mineral oil is very high. If further confirmation is required, it can be sent to the corresponding testing agency to use the national standard testing method for further identification.
Through sample collection and testing, the author found that some silicone sealant manufacturers on the market have adopted extremely irresponsible practices by mixing weather-resistant sealants with a considerable amount of cheap mineral oil instead of expensive organic silicon raw materials. To achieve the purpose of reducing production costs and obtaining market price advantages, it does not consider the serious quality problems and safety hazards caused by the decline in product quality. The user must be careful to identify during the selection process, and do not use these oil-extended sealants to cause losses.